Cameras which are used in driver assistance systems of vehicles are generally manufactured in a fixed-focus design, i.e., having fixed focusing. These cameras must be checked for a correct alignment of the image plane of the objective with the surface of the image sensor. For this purpose, a test pattern is generally recorded at various positions in the image field, which is projected by a motor-tunable collimator from various virtual object distances. The distance range may respectively be varied in multiple steps between infinite and 2 m in order to ascertain the object distance at which the test object is focused. An MTF (modulation transfer function) is advantageously calculated as a measure of the contrast for each position and for each object distance from the definable pulse response in the recorded image of the test pattern. The tuning of the object distance is also referred to as a through-focus scan.
The cameras are generally to be focused in such a way that the depth of field range reliably covers the relevant distance range for the driver assistance function. Generally, objects at a large distance and those at a shorter distance are to be imaged having sufficiently good contrast. This property is to be achieved at the different positions of the image field, i.e., including image regions which are farther apart, such as the corners of the imager and of the image provided by it.
The cameras are generally tested by rotating the camera and the collimator relative to each other in order to be able to record the test pattern in various image field positions. Thus, a support accommodating the camera or the collimator is rotatable or pivotable. Correspondingly, many runs of the tunable collimator are required at the different pivot positions.
If the camera to be tested or the collimator is rotated or tilted, an exact centering on the center of rotation of the alignment unit is required in each case. Generally, in such measurements, the test pattern is repositioned to another image field position as an external loop of the measuring procedure, and the through-focus scan is carried out as an inner loop, since the alignment of the test pattern is more time-consuming.
Measurements of this kind are therefore generally complex and require exact adjustments of the camera and/or the collimator in different pivot positions.
German Published Patent Appln. No. 10 2004 010 958 describes a device for manufacturing a camera, in which a first calibration field is accommodated in a support device and a second calibration field is provided for larger virtual object distances separately from the support device, the second calibration field being able to be detected by the camera via multiple mirror units accommodated in the support device. The position of the image sensor of the camera may be finely positioned using a hexapod robot. It is thus possible to implement larger regions of virtual object distances using the multiple calibration fields and the deflection device from the mirror units.